I didn't say it was easy. I was saying why he lost.
With his comp, the only hope for them killing Kog'maw was for Pantheon or Twisted Fate to surprise him from a bush. He lacked any champion capable of closing to him easily and bursting him. If he had had Talon, Akali, or Zed (the only three assassins I can think of that could get past their comp), or someone like LB or Ahri, his odds would have been pretty good, assuming he closed before Cho'gath got fed. The lack of that got him killed.
I was talking specifically about Kog'maw, however. Not Kog'maw with a Lulu. The only hope there is...well...a miracle. If you have someone like Xerath, who could possibly kill Lulu from long range, the odds would have been pretty good. But, with that comp...? No way.
Against Lulu, you have to kill her if she ults someone else. That's her counterplay. If she keeps someone else alive, you blow her face up. Just like if the enemy team has an overactive Soraka.
Cho'gath, his only real weakness is ban phase. Barring that, you have Vayne and Fiora. Without those...Nasus or Veigar, maybe? Maybe a Sion? Possibly a heavily-stacked Kindred? Without those...your only hope is to split-push them to death. Cho'gath's turret-taking powers leave a lot to be desired, at least.
And, as I said, to beat Kog'maw, just have someone jump in his face and nuke him. He's on the same defensive tier as Kindred and Vayne, but has no mobility, making him the weakest to burst there is. Even Sona has more durability than Kog'maw, and she's made of tissue paper.
You just have to find some way to combine these three things into one team. Someone like Akali will help a lot against Lulu and Kog'maw, as long as you get the W down before Lulu polymorphs you, since she's not locked into bursting one champion, meaning if Lulu ults Kog, she can burst Lulu, or visa versa.